The present invention relates to sheet-feeding apparatus in general and more particularly to an improved sheet-feeding apparatus for automatically separating sheets of material individually from a stack of such sheets and translating them to a predetermined position for further processing within the apparatus or in another machine.
While having wide applicability for use in processing sheets of various types, sizes and materials, such as paper, cardboard, metallic and plastic material and the like, the present invention is particularly suitable for feeding paper sheets into facsimile and office copier equipment.
Presently, a variety of paper stock is available and used by office personnel in such machines. The paper stock may vary widely in its stiffness, thickness, porosity, weight and surface characteristics. Zinc oxide coated paper, for example, which is used in many office copiers, is particularly awkward and difficult to handle in sheets because of its rough surface, stiffness and weight. It and sheets of other types of paper also have a tendency to cling together because of moisture, static electricity and the like. These characteristics, separately or together, frequently result in making it difficult to automatically, as well as manually, separate a single sheet of paper from a stack of such sheets.
On occasion, it may be desirable to load a machine with paper sheets of varying widths. On other occasions, office personnel may inadvertently misalign a fresh stack of sheets with respect to a remaining stack of sheets when replenishing a supply of stock in a machine. These circumstances also lead to difficulties in paper handling and may result in jamming of the machine.
The two basic functions of a sheet-feeding machine are to separate the first or top sheet in a stack from others in the stack, particularly from the second sheet with which it is in contact and to move the selected sheet to a predetermined desired position.
Two principal methods are presently employed for separating a top sheet from a second sheet. The first of these methods involves the application of a moving frictional surface to the top of the first sheet to slide it off the second sheet. This method is unreliable, however, because surface friction forces vary widely between various types of paper, and the driving friction applied to the top sheet may be less than that between the top sheet and the second sheet so that the second sheet remains fixed to the top sheet. In other instances, the friction between the top sheet and second sheet may exceed that existing between two other sheets in the stack, and the stack will separate at the lower friction interface so that all sheets above that point will feed together. Also, residual moisture or electrostatic attraction may be sufficient to stick the top two sheets of a stack so tightly that they are fed together. Zinc oxide paper, for example, because of its weight, relatively rough surface and the other problems mentioned, is particularly difficult to slide off a second sheet unless the top sheet is first lifted to separate them.
Thus, the second principal method of separating and moving sheets involves lifting the top sheet to separate it from the second sheet before attempting to slide it off the second sheet. For this purpose, vacuum cups and the like have been employed. The difficulty in such prior known apparatus, however, is that the second sheet still frequently follows the top sheet. This is due to the application of part of the lifting force to the second sheet as well as to the top sheet when, for instance, the top sheet is slightly porous. Under these circumstances, the vacuum may act strongly enough on the second sheet to lift it also. In addition, air rushing around the edges of the top sheet in such prior known equipment is frequently strong enough to lift the second sheet.
To avoid the problems associated with the use of friction belts, rollers and the like and the problems associated with prior known vacuum type sheet-feeding apparatus, more recent equipment has employed the use of adhesive fingers or arms for grasping a top sheet from a stack. While avoiding or reducing many of the aforementioned problems associated with prior known sheet-feeding apparatus, the newer equipment is, however, relatively costly to manufacture, operate and maintain by virtue of its complexity, and the need for continual cleanliness, and sufficient adhesiveness to perform its separating function.
In general, most, if not all, prior known sheet-feeding apparatus require time-consuming and skilled adjustments for the handling of sheets of differing material characteristics and sheet sizes as well as routine maintenance.